The mechanism of HPV transmission at the cellular level is poorly understood. Keratinocytes are the target cells for HPV infection. These cells normally exit the cell cycle and undergo the process of differentiation, including expression of proteins that become components of the cornified cell envelope (CCE). Loricrin, involucrin, small proline rich proteins (SPRs), cytokeratins, and other proteins are covalently cross-linked to make up the CCE. The endpoint of differentiation is a layer of flattened, durable, enucleated CCEs that provides the host with barrier protection. HPV infection does not induce cell lysis, and the mechanism of virion escape from infected keratinocytes is not known. The CCE in its normal, durable state would likely hinder virion release. We theorized that a defective CCE would facilitate release of virions. Our studies support this hypothesis. We have shown that HPV 11 infection induces abnormalities of CCEs, and that desquamated, cornified cells from HPV 11 infected tissue are effective transmitters of infection. We have also shown that the HPV 11 El^E4 protein is associated in vivo with the CCE. Our studies of the effects of HPV 11 infection on the CCE demonstrate a markedly reduced amount of Ioricrin and an abundance of SPR3 in HPV 11-infected epithelium. Our studies, performed on fully differentiated epithelium, suggest that HPV 11 gene products cause the defects in the CCE. In addition, our recent studies show that HPV 11 infection reduces Ioricrin transcription. The combined effects of HPV gene products on the CCE may facilitate the escape of virions, and thus increase the efficiency of HPV transmission. In the current proposal, we will test the hypothesis that HPV 11 induces defects of the CCE, and that these defects can be attributed to the effects of the El^E4 and E2 proteins. To test the hypothesis, we will 1) determine if the El^E4 protein is a TGase substrate or an inhibitor of these enzymes; 2) analyze the effects of El^E4 proteins on the composition and biophysical characteristics of CCEs, and 3) examine of the effects of the E2 on expression of the CCE proteins Ioricrin and small proline rich protein 3.